1. Field of the Invention
The invention relates to a charge/discharge protection circuit for a rechargeable battery, and more particularly to a charge/discharge protection circuit where the fusible links are melted sequentially allowing the use of a smaller area on an integrated circuit.
2. Description of the Related Art
Circuits have been described referring to charge/discharge protection circuits for a rechargeable battery comprising at least one rechargeable cell, with a control logic which opens or closes n parallel load current switches depending on the magnitude of the voltage at the battery terminals, the voltage at the charge/discharge terminals of the protection circuit, and the charge or discharge current. Where that control logic comprises an over-voltage detector which in case of an over-voltage disconnects the battery from the charge/discharge terminals through sequentially controlled melting of integrated, battery-side parallel coupled fusible links. Each of which can be coupled to the oppositely poled battery connection via an in series connected associated load current switch and an associated, controllable switch segment of a short-circuit switch array.
Such circuits are known from the above referenced Related Patent Applications, which is expressly referenced herewith. In particular, this circuit can be disposed between a single lithium-ion cell and the electronics of a mobile phone. It protects the battery, respectively the cell from a dangerous overcharge and can be produced with a significantly lower electric strength than is required in a worst-case scenario, and, therefore, at a favorable cost. In the case of an over-voltage, the fusible links will be destroyed individually one after another. The battery is thereby disconnected permanently from the over-voltage. The destruction of the protection circuit is knowingly accepted. To insure that the protection circuit is not already destroyed by the over-voltage before the last fuse has melted, the protection circuit comprises, parallel to the charge/discharge terminals, a semiconductor switch is immediately switched into its conductive state by the over-voltage detector in case of an over-voltage, so that the over-voltage collapses due to the short-circuit. Because the semiconductor switch for that reason must have a high current carrying capacity, it requires a comparatively large area of real estate on the chip and therefore increases its cost.
The task of the invention is to create a protection circuit of the above mentioned type which, while providing the same protection, can be fitted onto an area-wise smaller and therefore more economical chip.
Relating to the invention at hand is U.S. Pat. No. 5,703,463 (Smith) which describes the use of MOSFET switches and fail-safe elements such as fuses or circuit breakers to protect a battery from an overcharge. Other protection such as discharge protection are not considered.
Relating to the invention at hand are also two untranslated German patents:
DE 19737775 (Smith) is a translation of the above cited U.S. Patent.
DE 10149234 (Smith) describes a shunt control protected by a plurality of fusible links designed to insure that the fuses are activated, i.e., melted. This is achieved by using an operational amplifier with feedback.
Also related to the invention appears to be an untranslated Japanese patent 10-66251 where one drawing shows a parallel circuit of a fuse in series with a switching element with other components and a battery arranged around it.